The present invention relates to a laser diode and, more particularly, to a beam scannable laser diode for use as a light source of laser beam printers, optical disks and the like.
FIG. 6 is a cross-sectional view showing a typical structure of a conventional beam scannable laser diode. The prior art of the beam scannable laser diode will now be described with reference to FIG. 6.
An n-Al.sub.0.5 Ga.sub.0.5 As cladding layer 2, an AlGaAs multi-quantum-well active layer 33, a p-Al.sub.0.5 Ga.sub.0.5 As cladding layer 4, and a p-GaAs contact layer 5 are deposited consecutively on an n-GaAs substrate 1. Two striped current injecting regions are exposed at the top of the layered structure so that an SiO.sub.2 mask pattern 8 is formed thereon. Further on top of the layered structure are formed Au electrodes 16a and 16b arranged in parallel and spaced a predetermined distance apart. A common electrode 16c is formed at the bottom of the diode. The electrodes 16a and 16b constitute two coupled waveguides arranged in parallel. The light is confined to the active region 33 and guided by the cladding layers 2 and 4.
Injecting currents asymmetrically into the two coupled waveguides generates a mixed mode, i.e., an intermediate mode between even mode and odd mode of the light guided into the waveguides. Suitably controlling the injected currents deflects the scanning beam direction as needed.
The prior art of this field is described illustratively in the minutes of the International Conference on Solid State Device and Materials in Yokohama (1991), pp. 338-340.
The beam scan of the conventional beam scannable laser diode is accomplished by combining the above-mentioned two modes, even and odd modes. Given that characteristic, the conventional beam scannable laser diode must rely on a complicated optical system when applied to a device required to provide a single spot. The beam scan of the conventional laser diode is effected with a beam that is not collimated. Thus when an ordinary lens-based system comprising the laser diode is used to focus the beam, there occurs the problem of the focusing point staying unchanged while the beam is being deflected.